With the advent of technology to produce synthetic fibers that serve mankind not only by being more economical and stronger than natural fibers, but also by freeing up much needed agricultural land that heretofore had been needed to grow vast quantities of natural fibers, came a quest for a process that would impart to these synthetic fibers the same beneficial qualities possessed by natural fibers. The major quality that synthetic fibers lack, the one attribute that would make them cool and comfortable like the natural fibers, is the ability to substantially absorb moisture.
Throughout this application the terms "absorb" and "absorption" will be used to refer generally to the hygroscopic properties of the fibers and fabrics made therefrom. However, it will be understood that these terms refer to related hygroscopic properties such as adsorption, moisture transport, wicking, wettability, etc. Thus, although the term "adsorption" may be more appropriate for referring to the attraction of water to the outer surfaces of fibers per se, and the term "absorption" may be more appropriate for referring to the dispersal of moisture in the interstices between the fibers of a fabric, the term "absorption" will be used for convenience to refer to both phenomena.
The present invention satisfies this much sought after quest and provides to synthetic fibers permanent qualities once attributable only to natural fibers such as significant water absorbency, superior dye receptivity and anti-static qualities. At the same time, the present invention allows for the production of synthetic fibers that have superior soil release qualities.
It has been known in the prior art to attempt to graft-polymerize water-soluble monomers such as acrylic acid, acrylamide, and N,N'-methylene-bis-acrylamide (MBA) onto fibers to impart antistatic and water absorption properties to the fibers. However, such attempts at graft polymerization have been problematic due to the inability to obtain substantial or even any graft polymerization, a requirement of a long period of time, the tendency to form large amounts of homopolymers, and difficulties in controlling the process conditions. The raising and control of reaction temperature is extremely critical and sensitive to the formation of excess homopolymers. Excess homopolymers adhere to the inner walls of the processing equipment thus causing both a time and labor-consuming clean-up job. Also, disposal of the residue solution containing a large amount of homopolymers is a source of industrial pollution. Fabrics thus treated in an environment of excessive homopolymers have their surfaces coated with a thick homopolymer layer which imparts moisture-absorption and some antistatic properties to the fibers. Unfortunately, these properties are not permanent and are lost within about ten washings. Furthermore, excessive homopolymers tend to cause blotching on treated fabrics which interferes with acceptable commercial dyeing and results in inferior treated fabrics.
In an alternative polymerization process that comprises impregnating fibers with a solution containing a monomer and a polymerization initiator, such as peroxide or persulfate, and heating them, it takes a long period of time to start and advance the polymerization reaction; moreover, the polymers that adhere to fibers are removed quite easily by washing so that their antistatic and moisture-absorption properties can no longer be retained.
Still another process involves applying a water-soluble vinyl monomer together with a polymerization initiator to fibrous structures and heating them in a non-solvent of the monomer, such as hydrocarbons or the like. Such process has problems of industrial hygiene and workability including solvent recovery.
U.S. Pat. No. 3,313,591 to Tanner describes a process of graft polymerizing ethylenically unsaturated monomers to polycarbonamides to improve various properties of the polymer structure. Tanner uses a one step process using very long time durations (15 hours or more) and very high concentrations of monomer.
A more recent attempt to cure the deficiency in the prior art is disclosed in U.S. Pat. No. 4,135,877 to Aikawa et al. This patent also discloses a one step process of graft polymerizing certain selected vinyl monomers to polyamides or fiber structures. According to the process described in that patent, polymerization initiators are completely eliminated.
Other patents disclosing the graft polymerization of monomers to polyamides and other polymer structures include U.S. Pat. Nos. 3,097,185; 3,099,631; 3,252,880 and 3,278,639. However, the methods of these patents involve the use of ionizing radiation in the formation of a polymer melt in order to effect graft polymerization.
While many of these processes of the prior art result in improved antistatic, hygroscopic and dye receptive properties in the polymer, they have not been entirely successful commercially due to the difficulties in obtaining permanent and substantial results and other processing difficulties due to excessive formation of homopolymers which are difficult to remove from the final product and process equipment. Furthermore, some prior art methods require high concentrations of monomer, rather than low concentrations of monomer; and other prior art methods require long periods of time.
The possibility of improving such properties of synthetic fabrics in general, including but not limited to polyamides, is important since many of these fabrics exhibit characteristically undesirable properties such as static cling poor water absorbency, and poor dye receptivity. Hence, the commercial acceptance of nylon fabrics, for example, has been severely limited. Heretofore, I am aware of no commercially successful process which has resulted in a treated fiber having substantially improved antistatic, hygroscopic, and dye receptive properties which are permanent and can withstand repeated washings.
The principal object of the present invention is to provide a unique process and a product of that process which alleviates the past shortcomings of attempted graft polymerization.
The present invention is unique in that the process can be completed in very short periods of time, using a low concentration of chemicals, is not sensitive to changes in temperature, and forms relatively minute amounts of homopolymers and allows commercial products to be made which can be dyed and otherwise processed.
The product of the present invention is unique in that it is the first that has grafted onto fibers an economical, commercial, permanent, clean, and low add-on graft polymer.
Although the treatment method of this invention is particularly useful for nylon, which is not naturally absorbent and is subject to static electricity problems, it is also beneficial to enhance the properties of absorbent fibers such as cotton. Treating a blend consisting of cotton and synthetic fibers in accordance with the method of this invention may allow the use of less cotton in the blend to achieve a comparable fabric.